18 



HUTCHINSON'S POPULAR BOTANY 



-which consists of a net-work of threads (or nbrillce). embedded in a semi- 

 fluid substance known as nucleoplasm. The nucleus is not. however, a 

 necessary element : protoplasm may live, and move, and do work when no 

 nuclei are present. 



Once these cells were living cells not. indeed, alive in every part, 

 for that could be said of nothing that lives ; but they were living cells. 

 Each cell was a life-unit, for the mysterious principle of Life was in 

 each: and the protoplasmic contents of the cell, not the cell-walls, consti- 

 tuted the life-matter. Out of this apparently structureless matter the 

 cell-walls were formed, much as were the cellulose coats of our self- 

 dividing Sphcerella ; for in each case the protoplasm was the vital, active, 

 formative element of the cell. Did. then, these cell-walls cease to grow 

 when once they had been formed ? By no means. Yet their growth 



was due. not to any principle of 

 Life within themselves, but to the 

 introduction of fresh particles of 

 cellulose among those already 

 existing. And these fresh particles 

 were formed and added by the 

 protoplasm. 



The history of our fragment of 

 onion-skin is not singular. What 

 was once true of this little cluster 

 of cells, packed together in a space 

 no larger than a Lupin seed, is 

 true of all living organisms what- 

 soever, whether in the Vegetable 

 or the Animal world. The proto- 

 plasm is the essential part of the 

 cell. We would press this, even 



at the risk of being tedious. It is a point of all-importance. The granular, 

 structureless contents of the cell, and not the wall of cellulose, constitute 

 the unit, the elementary part or cell. The protoplasm produces from itself 

 the cellulose : the cellulose does not form the protoplasm. Cellulose, indeed, 

 is formed from three of the elements which enter into the composition of 

 protoplasm namely, carbon, hydrogen, and oxygen. The formula is CgH^O^ 

 Here, then, is proof from chemical analysis. When our Sphcerella was at 

 rest at the bottom of the drop of water, the source of all the vital changes, 

 it will be remembered, was the protoplasm, not the membranous coat that 

 invested it: Through this delicate coat, it is true, was drawn in from the 

 surrounding water the lifeless material which was required for the nourish- 

 ment and growth of the plant : but the interior substance was the active 

 -agent, the protoplasm was the drawing power : indeed, the same work went 

 on when the plant was a naked cell, without any cellulose envelope whatever. 



FIG. 35. CELLS OF ONION SKIN. 



-A fragment (much enlarged) of the delicate skin between the 

 firm layers of the onion bulb. 



